Perhaps you could ask neighbours not to let him in/feed him, (accompanied with a nice bottle of wine), and lie explain that he's on a special diet?
And Morph sounds like an extra special cat - can be hard to adapt to one not quite so affectionate. I read your posts about him... right up until the end. A huge cat shaped hole in your heart to fill.
The only advice I can suggest is ignore him. Fed, watered - the basics. Do you keep him in at night? (an especially good idea, as we have firework season upon us). Let him come to you, and try, hard as it is, not to compare him to your lovely Morph.
I understand it must be upsetting, after having a person oriented and affectionate cat. Does he show his affection in other ways? Like creeping into bed once you're asleep for instance? Does he like interactive games?
Purring doesn't necessarily equate happiness, cats purr for a variety of reasons. Grumpy MCat purrs if you just look at him, the only time Little M purrs is when he's DTD with his furry shag-bag, in spite of being a happy, bouncy little soul, and he scratches the duvet/my bare back to be let in under the duvet. He's not a lapcat though.
He's still in his teenage dickhead years, so hope is not lost!
There will be better experienced than me to advise in the morning, I'm sure.